1. Field of the Invention
A heating, ventilating and air conditioning (HVAC) system having a vibration isolation mechanism is provided to isolate vibrations of the motor.
2. Description of the Prior Art
Blower motors create a torsional vibration during their operation which can cause excitation of the HVAC module and thus noise. It is especially desirable in cooling air moving systems, to isolate vibrations originated by motor operations due to the intensifying effect of both the housing and the air conveying ductwork.
The torsional vibration created by a blower motor is related to the torque pulses that rotate the armature each time the current flows through the windings as the brushes contact the commutator bars. Since blower motors operate over a speed range (typically 1000 rpm to 4000 rpm), a fairly wide frequency range of the input torsional vibration is created. For example, a motor with 12 commutator bars will create torsional vibration from 200 Hz to 800 Hz as the motors speed sweeps from 1000 rpm to 4000 rpm.
These vibrations can create noise and to prevent noise problems, it is common to isolate the motors from the HVAC module. Isolation in effect lowers the natural frequency of the mechanical system such that input energy is attenuated in the problem frequency range.
To do this in HVAC motor applications it is common practice to use rubber materials to isolate the motor from the HVAC module. However, rubber isolation requires extra parts, extra processing and extra assembly and usually labor. Thus, rubber isolation adds cost. In addition, rubber isolation generally lowers stiffness in several directions which can cause increased vibration by shifting the resonant torsional mounting frequency below 200 Hz. It will also lower the radial mounting frequency which may amplify the 1st order unbalance forces in the 16-67 Hz range.
In order to overcome some of the disadvantages of rubber isolation, radially extending plastic spokes have been designed to provide desired torsional stiffness to attenuate torsional vibration. However, for most motors the radial spokes will add considerable effective diameter to the motor assembly thus decreasing package density thereby increasing shipping costs. In addition a separate plastic sleeve or harness is needed on the motor to attach the plastic spokes.
Examples of isolation systems include U.S. Pat. No. 6,897,580 to White, U.S. Pat. No. 3,746,894 to Dochterman et al., and U.S. Pat. No. 4,200,257 to Litch III.
White describes a method of providing isolation via radially extending plastic spokes which extend outwardly from a sleeve surrounding the motor and are integral to the sleeve. Additional damping elements are disposed at the distal ends of each spoke and extend axially to form a connector for connecting the assembly to a casing. The casing has recesses for engagement with the spokes.
Dochterman describe a vibration isolation system having a rigid sleeve surrounding the motor, and a vibration isolator having a top and a bottom disposed between two clamping elements. Both clamping elements are secured to a casing and are disposed on the ends of the vibration isolator which is a rubber dumbbell shaped member. A support extends from the sleeve and is secured to the isolator between the top and bottom.
Litch III teaches an isolation system that uses three torsionally flexible post springs extending radially outwardly from the motor at an upward angle toward a casing. The post springs are pivotably secured to the casing.
Although the prior art effectively reduces the transmission of vibrational pulses, there is a continuing need for a cost effective means of reducing the transmission of vibration pulses while simultaneously maintain a desired radial and axial stiffness. Specifically, arms or posts that reduce package density and that achieve a desired stiffness are needed.